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Unit B
Understanding Animal
Body Systems
Lesson 1
Understanding Animal Digestion
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Terms
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Absorption
Amino acids
Anus
Avian
Bile
Cecum
Chyme
Crop
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Cud
Digestion
Digestive system
Enzymes
Eructated
Feces
Gizzard
Intestinal juice
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Terms
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Monogastric
Omasum
Organs
Pancreatic amylase
Pancreatic juice
Pepsin
Polygastric
Pseudo-ruminant
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Reticulum
Rumen
Ruminant
Rumination
Salivary amylase
Salivary maltase
Stomach
Trypsin
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What are the various types of
digestive systems found in
animals?
Knowledge of the different types of
digestive systems is critical in
selecting the proper feeds for
livestock. Understanding the
chemical and physical changes that
occur during the digestion process
leads to more efficient livestock
feeding.
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
Digestion is the process of breaking
down feed into simple substances that
can be absorbed by the body.
 Absorption is taking the digested parts
of the feed into the bloodstream.
 The digestive system consists of the
parts of the body involved in chewing
and digesting feed.
This system also moves the digested feed
through the animal’s body and absorbs the
products of digestion.
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Different species of animals are better able
to digest certain types of feeds better than
others.
This difference occurs due to the various
types of digestive systems found in animals.
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There are four basic types of digestive systems:
1. Monogastric (simple)
2. Avian
3. ruminants (polygastric)
4. pseudo-ruminants.
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A.
A monogastric digestive system
has a simple stomach.
 The stomach is a muscular organ
that stores ingested feed and moves
it into the small intestine.
 The stomach secretes acid.
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The acid results in a low pH of 1.5 to
2.5. The low pH destroys most bacteria
and begins to break down the feed
materials.
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Monogastric Digestive System
 Animals with this type of digestive
system are better adapted to the
use of concentrated feeds, such as
grains, than the use of large
quantities of roughages.
 Examples of monogastric animals
are dogs, cats, and humans.
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Monogastric Digestion
The digestive system of a dog
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B.
The avian digestive system is found
in poultry.
 This system differs greatly from any other
type.
 Since birds have no teeth, there is no
chewing.
 The esophagus empties directly into the
crop.
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The crop is where the food is stored and soaked.
 From the crop the food makes it way to the
gizzard.
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Avian Digestive System Continue:
 The gizzard is a very muscular organ,
which normally contains stones or grit
which functions like teeth to grind the
food.
 Digestion in the avian system is very
rapid.
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Avian Digestive System
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Avian Digestive System
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Ruminant Digestive System
C.
The polygastric or ruminant digestive system has
a large stomach divided into compartments.
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The rumen is the largest section of the stomach.
 The rumen contains bacteria and other
microbes that promote fermentation.
 The rumen is the first compartment of the
stomach that food enters.
The polygastric system is designed for food to
be ingested, eructated (belched up), chewed,
and swallowed again..
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Ruminant Digestive System
Locate the Rumen
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Ruminant Digestive System
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The reticulum is the second segment of
the stomach.
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The reticulum is sometimes called the
“honeycomb” due to the structure of its
wall and location.
This is a picture of an actual
reticulum. Notice the
honeycomb texture.
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Ruminant Digestive System
– The third portion of the ruminant digestive
system is the Omasum.
– The Omasum is shaped like a small
cabbage.
– The omasum is a small compartment that
acts as a filter of materials for the fourth
compartment.
– The omasum is also known as “manypiles”.
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Ruminant Digestive System
This is a
picture of an
omasum.
Notice the
folds on the
exterior.
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Ruminant Digestive System
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The abomasum is the fourth and
final compartment to the ruminant
digestive system
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The Abomasum is often considered the
true stomach. It functions just like that
of the simple-stomached animals.
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Ruminant Digestive System
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The abomasum secretes gastric
juices that kill the microbes that
have passed with the food
materials from the rumen.
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The abomasum also contains
hydrocholoic acid and enzymes that
break down feed materials into simple
compounds.
These simple compounds can be
absorbed by the stomach wall and the
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intestines.
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Ruminant Digestive System
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The polygastric system uses feed high in
fiber.
Thus, these animals make good use of
roughage.
Some examples of polygastric or
ruminant animals are cattle, sheep and
goats.
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Ruminant Digestive System
Rumen – Largest, fermentation occurs here
Reticulum – honeycomb structure
Omasum – Filter, known as manypiles
Abomasum – True Stomach
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D. A pseudo-ruminant is an animal that
eats large amounts of roughage but
does not have a stomach with several
compartments.
 The digestive system does some of
the same functions as those of
ruminants.
 They are able to utilize large
amounts of roughages because of
the greatly enlarged cecum and
large intestine.
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Pseudo-ruminant Digestive System
Continued:
 These animals often eat forages as
well as grains and other
concentrated feeds.
 Examples of pseudo-ruminants are
horses and rabbits.
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Pseudo-ruminant Digestion
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What are the major parts of the
digestive system and their functions?
II.
The digestive system is made up of a
number of parts known as organs.
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The system beings at the mouth, where
food enters the body, and continues
until anus, where undigested material
exits the body.
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The digestive systems of most livestock
are very similar in terms of the organs
they contain.
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A. Mouth and Esophagus
 The chewing action of the mouth
and teeth breaks, cuts, and tears up
the feed.
 This increases the surface area of
the feed particles which aids in the
chewing and swallowing process.
 Saliva stimulates the taste of the
feed but also contains the enzymes,
salivary amylase and salivary
maltase.
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Mouth and Esophagus Continued:
 Enzymes are substance called
organic catalysts that speed up the
digestive process.
 Salivary amylase changes starch to
maltose or malt sugar.
 Salivary maltase changes maltose
to glucose.
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B. Ruminant Stomach
 The four parts of the ruminant stomach
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are rumen, reticulum, omasum, and
abomasum.
They do not chew much of their food
before swallowing.
The solid part of food goes into the
rumen. The liquid part goes into
reticulum, then the omasum and on into
the abomasum.
In the rumen, the solid feed is mixed and
partially broken down by bacteria.
When the rumen is full, the animal lies
down. The feed is then forced back into
the mouth rumination occurs.
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Ruminant Stomach
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Ruminant Stomach Continued:
 Rumination is the process of chewing
the cud.
 Cud is a ball-like mass of feed that is
brought up from the stomach to be
rechewed.
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On average, cattle chew their cud about six to
eight times per day.
A total of five to seven hours each day are
spent in rumination.
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Ruminant Stomach Continued:
 The rumen and reticulum contain millions
of bacteria and protozoa. It is the
bacterial action in the rumen that allows
ruminants to use large amounts of
roughage.
 These bacteria can change low-quality
protein into the amino acids needed by
the animal.
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Amino acids are compounds that contain
carbon, hydrogen, oxygen, and nitrogen.
Amino Acids are essential for growth and
maintenance of cells.
 Bacteria also produce many of the
vitamins needed by the animal.
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C. Monogastric Stomach
 When feed enters the stomach of
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monogastrics or the abomasum of
ruminants, gastric juices begin to flow.
The fluid comes from glands in the wall of
the stomach.
The juices contain from 0.2 to 0.5 percent
hydrochloric acid.
This acid stops the action of the amylase
from the mouth.
These gastric juices also contain the
enzymes pepsin, rennin, and gastric
lipase.
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Monogastric Stomach Continued:
 Pepsin breaks the proteins in the feed
into proteoses and peptones.
 The muscular walls of the stomach churn
and squeeze the feed.
 Liquids are pushed on into the small
intestine.
 The gastric juice then act on the solids
that remain in the stomach.
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D. Small intestine
 The partly digested feed that leaves the
stomach enters the small intestine.
 It is an acid, semi-fluid, gray, pulpy
mass.
 This material is called chyme.
 In the small intestine, the chyme is mixed
with three digestive juices: pancreatic
juices, bile, and intestinal juice.
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Pancreatic Juice Continued:
 Trypsin breaks down proteins not broken
down by pepsin.
 Some of the proteoses and peptones are
broken down by trypsin to peptides.
 Proteoses, peptones, and peptides are
combinations of amino acids.
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Proteoses are the most complex compounds
and peptides are the simplest.
 Lipase works on fats in the feed. It
changes them into fatty acids and
glycerol.
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Pancreatic Juice Continued:
 Pancreatic amylase changes
starch in the feed to maltose.
 Sugar and maltose are then broken
down even further by maltase.
 They are then changed into a simple
sugar called glucose.
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Bile
2. Bile is a yellowish-green, alkaline,
bitter liquid produced in the liver.
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Bile is stored in the gall bladder in all
animals except horses.
Bile aids in the digestion of fats and
fatty acids.
It also aids in the action of the enzyme
lipase.
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Intestinal Juice
3. Glands in the walls of the small intestine
produce intestinal juice.
 This fluid contains peptidase, sucrase,
maltase, and lactase, all enzymes used
in digestion.
 Proteoses and peptones are broken
down by peptidase into amino acids.
 Starches and sugars are broken down
by sucrase, maltase, and lactase into
the simple sugars, glucose, fructose,
and galactose.
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E. Cecum
 The cecum or “blind gut” is found where
the small intestine joins the large
intestine.
 It is a small organ and has little function
in most animals, except
pseudoruminants.
 In these animals, roughage feeds are
digested by bacterial action in the cecum.
F. Large intestine
 The main function of this organ is to
absorb water.
 Material not digested and absorbed in the
small intestine passes into the large
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intestine.
Large Intestine Continued:
 Feed materials that are not digested
or absorbed are called feces.
 This material is moved through the
large intestine by muscles in the
intestinal walls.
 The undigested part of feed is
passed out the body through the
anus, the opening at the end of the
large intestine.
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Review / Summary
1. What are the various types of
digestive systems found in animals?
2. What are the major parts of the
digestive system and their functions?
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